Magnesium alloy



MAGNESIUM ALLOY DanielGardner, NewYork,-N. Y.

N Drawing. Application August 3, 1953 Serial No. 372,170

1 Claim. (Cl. 75-168) keep the alloy as light as possible and at thesame time achieve satisfactory physical properties without upsetting theequilibrium between the ingredients which enter into a finallyacceptable formula.

Magnesium is abundant in nature and belongs to the group ofraw'rnaterials which are plentiful in theouter shells of the earth. Withits low density of 1.74 itis available for many purposes where such alight metal'is desirable. In accordance with my invention I am able toutilize the lightness of magnesium by achieving chemical and physicalproperties in a magnesium alloy without materially departing from thelow density of magnesium. In doing this, I am able to bestow upon themagnesium alloy the physical, chemical and physico-chemical propertieswhich magnesium itself does not possess. I am able to accomplish this,as mentioned above, without departing substantially from the density ofthe prevailing ele ment in the alloy, i. e., magnesium.

Before proceeding with the description of the present invention thefollowing table of some of the pertinent elea't Patent 2,823,996Patented Feb. 1 8, 1 1958 Aluminum is desirable for many purposes,particularly aircraft needs and can be alloyed in desirable ways.However, notwithstanding the properties that can be achieved byalloying, it is not possible to go very much below its density of 2.7.In instances where a lighter alloy is' desirable aluminum cannot be usedas the entire base.

In accordance with my invention, I obtain an alloy having a density notappreciably different from the density of magnesium, but having markedimprovements over magnesium in terms of physical and chemicalproperties, whichovercome the inherent weaknesses of magnesium asindicated in the above table.

The magnesium alloy of my invention comprises four essential'components:(1) pure magnesium as the primary component, a minor part of which maybe replaced by aluminum insome insta'nees if the increase density of thealloyfor the wantedpurpose is not objectionable; (2) asmall amount of aninterstitial metal; (3) a small but requisite amount of a filler for theinterstices of the interstitial metal selected from the group consistingof silicon or boron or both, preferably silicon in most instances; andin some instances antimony alone or in admixture with silicon and/orboron; and (4) a small but requisite amount of an auxiliary metalselected from the group consisting of calcium, beryllium, chromium,cobalt, nickel, manganese and yttrium, which facilitates theincorporation of the silicon or other third component.

The term interstitial is used to refer to an element capableof forming acompound with metalloid elements in which the metalloid atoms occupy theinterstices between'the at'omsof the metal lattice.

Thefollowing is a brief discussion of each of the four components (1)The properties of the pure magnesium, or magnesium a minor portion ofwhich has been replaced by aluminum, are we'll'known together with themanner in which they'aremade and can be utilized as the primarycomponent of my alloy. These need not be furments and some of theirproperties may be noted: 40 ther explained. The magnesium, and aluminumif it is TABLE I E1 e t Densit; Hardness oin oin a lo 0 asm n y (MP),(BP), BP/Ml ticity B 111 1.85 6.9 .27 1 350 1, 550 1.13 B35111??? 2. a9. 5 .24 2: 300 2, 500 1.1 Magnesium 1. 74 2 87 651 1, 110 1. 7 Aluminum2. 7 2. 9 659 2, 450 a. 7 Silicon 2. 4 7. 0 .34 1, 420 2, 600 1.8Calcium 1. 55 1. s 1. 03 845 1, 240 1. 47 Antimony s. 68 3. o 2. 2 6501, 380 2. 2

From this table it will be seen that magnesium has-a desirably lowdensity. However, it has an undesirably low melting point and lowboiling points, as well as a low ratin of boiling point to meltingpoint. In addition, it has a relatively low modulus of elasticity.

used, must be pure and have boiling points of 1110 C. and 2450 C.,respectively.

(2) The interstitial metals which are listed as the second component ofmy alloy, and their properties are as follows:

TABLE II Hard- Melting Boiling Modulus of De1]1)s)lty 1213s; D/H (ED21131: a??? BP/MP Elasticity p. s. C. O.

All of the elements above listed belong to the so-called transitionmetals of the periodic table, and are shown in the above listing as theystand in the vertical columns of the fourth, fifth, and sixth groups ofthe periodic table. Of the interstitial metals I prefer for the purposeof my invention titanium, columbium and tantalum, but

4 first two mentioned as the fourth component of my alloy, and theproperties of which are listed in Table I, I may include as the metalsfunctioning as the fourth component, as mentioned heretofore, chromium,cobalt, nickel, manganese and yttrium. Their properties are shown in thefollowing table:

any can be used alone or in admixture with each other.

The interstitial metals according to my experience, can all be obtainedby reducing their oxides by pure magnesium, with the exception ofthoria. Also, their halides are reduced by magnesium and a pureinterstitial metal is obtained.

.t has long been known that the interstices of the interstitial metalsare filled with metalloids and other elements such as hydrogen, oxygenand nitrogen. Halogens may also fill the interstices as well as carbon,sulfur, selenium and tellurium.

(3) In the magnesium alloy of my invention, containing an interstitialmetal, I have made the important observation that silicon and/ or boronand/ or antimony can fill up the interstices of these interstitialmetals, thus preventing the air, gases and other elements mentionedabove from occupying the instertices. Silicon is generally preferred asthe third component of my alloy, although any of the three may be usedor mixtures of two or three. Hereinafter I will refer to silicon asrepresenting the best embodiment but it is to be understood that in allreferences to silicon hereinafter, prior to the illustrative example,boron and antimony or mixtures thereof may be substituted for a part orall of the silicon.

Silicon is of interest in this connection because the interstitialmetals can readily be converted to their respective silicides wherebythe interstices of the metals are filled with silicon or boron orantimony if these are employed in their purification. it is importantduring all of such operations to avoid working with products containingmoisture, and it should be removed entirely by calcining. and theircompounds and salts is essential.

Silicon is not directly soluble in magnesium, only about 0.003% beingsoluble at 600 C. While the presence of the silicon increases thehardness of the magnesium alloy up to about 5 for the magnesiumsilicide, the problem is presented as to the easy incorporation ofsilicon in magnesium.

(4) it is because of this problem that I introduce the fourth componentin my alloy, which plays the important function of facilitating theintroduction of silicon into the magnesium alloy. Thus, for instance,calcium is included as a metal representative of the fourth component ofthe alloy, because it not only lowers the density of the magnesium alloycontaining it, but because silicon is easily introduced in calcium withthe formation of CaSi which has a density of 2.46, a hardness of 3.5 anda melting point of 1020". This formation is easy and goes according tothe following equation:

2Si+Ca CaSi +224.6 calories Also complete absence of alkaline metalsChromium, magnesium, cobalt and nickel, in addition to being utilized astheir silicides similar to that of the calcium and beryllium, may alsobe used to increase the modulus of elasticity and the generalworkability of the alloy. While their density is far greater than thatof magnesium or of calcium or beryllium, their introduction so muchimproves the metal that it can be used for other purposes and theincrease in the density is not so great as to make this undesirable forsuch purposes. In addition only small amounts are used so the increasein density is negligible.

Amongst these metals I should like to mention particularly yttrium,which has the properties of the metals mentioned in the previousparagraph, and is of special interest because it crystallizes in ahexagonal-system like magnesium. This element is often found in theinterstitial metals and such minerals as those containing titanium andtantalum, colnmbium and uranium. Yttria is reduced by magnesium to metalaccording to the following equation:

2 2+ g- 2Y+3MgO+77.4 calories The silicon plays a number of roles in thealloy which can be summarized as follows: (1) It forms silicides withmagnesium, the interstitial metals and the additional metals, in whichthe ratio of the silicon to the metal is 2:1; (2) silicon fills theinterstices of the interstitial metals, such as titanium, zirconium,tantalum, molybdenum, etc, which renders the use of the interstitialmetals suitable for the purpose of obtaining the high grade magnesiumalloys and solid solutions; (3) the silicon forms a silicide withcalcium which facilitates the obtention of the molten alloy providing aneven distribution of the individual ingredients whereby the mechanicalproperties of the alloy are improved; (4) the structure of the silicidesare exactly similar to that of the alloy, the bonds of the silicon atomsremaining unaltered and appearing exactly as in the case i of silicon;(5) not only does the silicon form silicides with the magnesium andcalcium, but also with any other metals that may be included, such asaluminum, chromium, manganese, nickel, cobalt, yttrium, and these may beprepared in the silicide form; (6) the silicon acts as a scavenger inthe initial stages of preparing the silicides so that allowance shouldalways be made for a certain percent loss during the process in whichsilicon is in- :cluded.

The relative amounts of the ingredients comprising the alloy aregenerally as follows:

(1) At least of the alloy is magnesium which forms the alloy base, or ifa portion of this is substituted by aluminum the magnesium-aluminummixture comprises at least 90% of which the magnesium in the alloywhich, as will be seen further, is desirable, Magnesium silicide issoluble in the presence of calcium silicide.

In addition to calcium and beryllium, which are the base is the primarycomponent.

(2) The interstitial metal which comprises the second component of myalloy should be present in an amount of 0.01 to 2.0% preferably 0.01 to1.0%.

L relation to preferable ratio is 0.01% beryllium'to 3% silicon. Whenchromium is introduced into any specific alloy it pref- (3) The silicon(or boron orantimony aonmiXture thereof) may be present in an amount of1.0 to 5%.

(4) The elements comprising-the fourth group vary in amounts dependingsomewhat upon the metal selected from this group. ln-the'case ofcalciumlarger amounts can be -employed, i. --e., -amounts up to 7.99%When beryllium is included 'it may bepresent in :amounts 1 of 0.001% to0.005 --When-the other-metalsof the fourth component-are includedtheymaybe-present in an amount it of 0.01%-to Z-%,-preferably 0.01-%-to1.0%.

-It is preferred that whenber-yllium is employed as a component itsamount should be kept relatively low in the amount, of silicon sothat-the maximum erably should be not more than-1 mol of chromium for 2mols of silicon. If yttrium is. included in the formula its relation tothe amount of silicon preferably should be chosen so that not more thanone part yttrium is present to .20 .parts. .ofsilicon.

The method of making thealloy. does not involveany particularcomplications. Theingredients .forming .the alloy .arebroughttogetherinafluid.phase,..either liquid or-gaseous. .In..view. of thenatureofmagnesitu'n, some of thewwork must becarried outinan atmosphereof an inert gas such as helium, argon, neon or the like. Work-1ng"invacuo,because it is rather expensive,-sl1ou1d be avoided ifpossible, but can be employed if this is-feasib'le mechanically andeconomically.

"In perfecting the alloy, at least a part of the silicon (or boron orantimony) should be addedto the bulk of the magnesium in the form of aternary alloy such as, for instance, a silicon-calcium-magnesium alloy.The interstitial metal or metals can be added in combination withsilicon asha .silicide. .A ,magnesium;siliconetitanium alloy representsone of thepreferred.fotmsm a g t .first threetcomponents of the alloyofmyinvention. A aquaternary alloy can also be producedby introducingcalciumsilicideor titaniumsilicide and then introducing the latter intoa molten bath containing pure magnesium in addition to which is. added asolid. solution of the calcium-magnesium alloy.

-Iintentionally avoid copper as an element in my alloy because copperweakens the resistance of magnesium to corrosion. The following examplesareillustrative of the invention:

Example 1 Percent Magnesium 95.00 Titanium .10 Silicon 4.60 Nickel .15Chromium .15

This alloy can be made by first preparing the silicides of nickel,chromium and titanium and adding these to the, remaining siliconwhereupon this mixture may be. in-

troduced into the molten magnesium with the adequate precautionarymeasures mentioned heretofore. The alloy has a melting point far higherthan themelting point of magnesium and has good resistance to corrosionand asubstantial increase in modulus of elasticity as compared Withmagnesium. All of thespeciiic examples hereinafter share. in theseproperties.

Example 2 Percent Magnesium 90.00 Tantalum .01 Silicon 2.35 Calcium 7.50Manganese .10 Chromium .02 Nickel .02

In this example the introduction of calcium into the alloy 1g reatly-.simpli fies the introduction of silicon. The other ,metals. areprepared as ,silicides ,and introduced. ,into the final charge workingin an atmosphere of an inert gas. The manganese in this6X8Illli2zlfifil1d in other examples containing it increases theresistance of magnesium to corrosion and facilitates its weldability.

Example 3 .Percent Magnesium 90.00 Columhiu m .02 :Sili on V 72.3.5Calcium 7.50 'Yttrium .23

This example is interesting and important: because it introduces theelement yttrium, an element as plentiful as vanadium, nickel, and zincin the outer shell of the earth. In addition, this element often occurswith columbium,

tantalum and titanium and can be introduced into the alloy Withoutseparation. The low melting magnesium 651 C.) is greatly fortified bythe higher melting yttrium (1490 C.). Yttrium, in addition, has the samecrystal- ;line structure as magnesium and beryllium, and since it:follows the other two metals in the table of electromotive arrangement,it provides a strongly positive alloy.

Example'4 Percent Magnesium 90.00 Titanium .02 Silicon 2.35 Calcium 7.50 Yttrium .23

This example is similar to Example 1 except for the inclusion of calciumand yttrium and differs from Example 3 by substituting..titaniumfol-columbium. The alloy. has the advantagesimparted by titanium andyttrium and the alciumiacilitatfis the introduction and interaction ofthesehelementsinto,the alloy along with the silicon. v1t also has .ahigher melting point and better" resistance to wear .and tear.

Example 5 Percent Magnesium 97.05 Zirconium .02 Silicon 2.78 Manganese.10 Chromium .05

In thisexample zirconium replaces titaniumand all of the metals,.zirconium, manganese and chromium are present .as slicides.

The introduction ofmanganese, which together with vanadium is firstconverted into a silicide, greatly facilitates the formation of a stablealloy. The melting point of vanadium silicide is quite high, namely,1654 C. and this property is imparted to the alloy. In addition, thealloy has marked hardness as compared with magnesium.

This example is similar to Example 6 except that a part of themolybdenum is replaced by tungsten, and manganese replaces nickel.

Example 9 Percent Magnesium 98.20 Titanium .01 Columbium .01 Silicon1.73 Manganese .05

This example is somewhat similar to Example 3 except that calcium andyttrium are replaced by manganese and titanium. The alloy is resistantto wear and tear, resist corrosion admirably and. has improvedmechanical properties. If desired the columbium can be replaced bytantalum.

Example 10 Percent Magnesium 98.20 Titanium .02 Tantalum .01 Silicon1.70 Beryllium .01 Manganese .06

All of the metals, including beryllium, are present in the form ofsilicides. The alloy is stable, has a high melting point and resistscorrosion. It also has a high and stable modulus of elasticity.

This alloy is unique because calcium and cobalt both have the samecrystalline structures. Boron also forms the compound Mg B whereby theboron and magnesium unite readily and directly.

Example 12 Percent Magnesium 98.00 Titanium .01 Tantalum .01 Silicon1.74 Nickel j .02 Chromium i l Q .02

Thisalloy is similar to Example 10 except that the beryllium andmanganeseare replaced by chromium and O (:1 nickel. All of the metalsare present in the form of silicides and give a very efiicient alloy.

Example 13 Percent Magnesium 65.50 Aluminum 32.50 Tantalum .01 Silicon1.70 Manganese .25 Chromium .02 Nickel .02

This alloy is of particular interest since it shows the possibility ofincorporating magnesium into aluminum and vice versa, withoutintroducing transition metals other than the interstitial ones.

Example 14 Percent Magnesium 60.00 Aluminum 30.00 Titanium 0.20 Silicon1.75 Calcium 7.40 Manganese 0.25

This example is similar to the previous example except that calcium isintroduced into the alloy. Calcium is a splendid diluent and isespecially useful in this alloy because it possesses two structures, i.e., that of both magnesium and aluminum.

Example 15 Percent Magnesium 96.00 Titanium .01 Antimony .25 Silicon3.49 Titanium .01

Inasmuch as antimony dissolves in molten silicon it is best prepared thesilicide SbSi This is then introduced into the molten titanium (whichcan be replaced by tantalum, columbium, zirconium, or vanadium,separately or in admixtures) followed by introducing the ternary alloyinto the molten magnesium adding it in small portions with the stirringafter each addition. These alloys show a marked increase in modulus ofelasticity, general improvement in mechanical properties, and alsogreater resistivity to corrosion.

The above light alloys, based on magnesium of high purity, into whichsmall amounts of the specified elements have been introduced, play animportant role in light weight metal construction, where resistance towear and tear and other chemical and physical properties are demanded.These alloys may be processed by recognized techniques such asquenching, annealing, aging, etc., as will be obvious to one skilled inthe art.

I claim:

An alloy having the following composition:

(Other references on following page) ear-3399s 1 Chambers TechnicalDictionary, pub- Sauerwald et a1. Oct. 22, 1940 Tweney et a1; Canac etal June 30, 1942 lished by the Macmillan C0., New York, N. Y. (1944),page 456. FOREPGITI PATENTS Merlub et al.: Metals and Alloys Dictionary,pub- Great Brltagn Oct 16, 1930 5 lished by Chemical Publishing 00.,Brooklyn, N. Y. Great Britain Apr. 12, 1939 (1344), page 116. OTHERREFERENCES Serial No. 420,578, Canac et al. (A. P. C.), published July13, 1943.

